1. Field of the Invention
This invention relates to a roller bearing capable of preventing stress concentration and useful as a bearing for installations and/or apparatuses which are required for a long-term operation and high reliability.
2. Related Background Art
In a roller bearing, for example, such as a self-aligning roller bearing, radius (R) of a corner of a spherical roller, i.e., radius of curvature (Rk) of a boundary portion between a rolling surface and a chamfer portion of the spherical roller (FIG. 2) has not yet been noted up to the present. Thus, conventional roller bearings including a self-aligning roller bearing had the following disadvantages.
As shown in FIG. 2, if the radius of curvature Rk of the corner edge 30 of the roller 20 contacted with a race 10 is smaller than an optimum value, when the bearing is subjected to a load, the stress is concentrated to this corner edge, thus reducing the rolling fatigue life, and increasing the wear or generating the seizure in certain circumstances.
To the contrary, if the radius of curvature Rk of the corner edge of the roller is larger than the optimum value, when the bearing is subjected to a heavy load, the corner edge cannot act as stress relaxation means and thus the stress is concentrated around the corner edge, thereby reducing the rolling fatigue life, and increasing the wear or generating the seizure in certain circumstances, as in the above case.
In order to obtain the optimum stress distribution, a technique in which a so-called "crowning" is adopted for reducing the radius of curvature of a portion adjacent to both ends of the roller has been proposed, for example, as disclosed in the Japanese Patent Publication No. 52-49541. However, in this case, if the radius of curvature of the corner edge of the roller has not the optimum value, in some cases, the stress relaxation by means of the crowning cannot effectively be achieved according to load.